1. FIELD OF THE INVENTION
This invention relates to a finger actuating device in a transfer press in which workpieces to be processed are successively transferred from a station to the adjacent one, thus completing a finished part.
2. DESCRIPTION OF THE PRIOR ART
The opening/closing action of fingers in a conventional transfer press is performed through hammering motion of a spreader mounted on an upper punch block or on a movable stripper. This hammering motion, however, involves a number of problems. Certain improvements contrived in this regard are disclosed in Japanese Patent Laid-Open Nos. 58-212507 and 62-16829.
In the device disclosed in Japanese Patent Laid-Open No. 58-212507, engaging fingers and transfer slides are driven by a drum cam, so it is impossible to adjust the relative timing of their movements. Further, since the operating condition of each engaging finger actuated by the drum cam cannot be adjusted, each finger opening/closing timing cannot be adjusted relating the movement of the transfer slides. Furthermore, since the direction of movement of the actuating bars is perpendicular to the finger opening/closing direction, it will be seen that it is difficult to get a larger stroke. If a larger stroke is needed, the width of the transfer slides must be enlarged. In addition, since the opening and closing movement of the fingers is effected by means of straight linear cams, ideal movement characteristics cannot be obtained. As for the device disclosed in Japanese Patent Laid-Open No. 62-16829, the crank arm operating the fingers is fixed to a rod with key, so the actuating timing adjustment thereof is not possible. Accordingly, the finger actuating timing of each station cannot be adjusted relating the movement of the transfer slides. As a result, it is not possible in the device disclosed to establish an optimum workpiece engaging condition of the finger tools related to the drawing action performed by a punch and the movement of the transfer slides.
By way of example, FIG. 1 shows a drawing process layout, a UM-3 type battery case in this case, on a transfer press. In the example shown, the first drawn height is 15.5 mm, the final one being 50 mm and there exists a difference of 34.5 mm between the first and the final drawn height. It will be seen that each drawing punch should have different length in accordance with the height of each workpiece at each processing station. This implies that the time when the punch strikes the bottom of the workpiece transferred on the common transfer level (die level) differs each other. Workpieces are drawn into the dies by the action of the corresponding punches, and are pushed out by knockout tools up to the die level, i.e., the transfer level, the bottoms of the workpieces being on the same level. Since the workpieces have individual different height, the time when they have been lifted up onto the transfer level to be transferred differs at each station.
Consequently, if the opening/closing time of the finger tools is the same throughout all the stations, shorter workpieces have to remain for a certain period without being held until the taller ones have been engaged by the fingers. This requires other provisions to hold workpieces. The best condition is that the fingers are opened when the lower end of the punch has drawn a workpiece by several mm into the die, and are closed when the bottom of the processed workpiece has been lifted up to the transfer level by the knockout tool.
In view of the characteristic in the transfer process described above, it is desirable that the finger actuating timing can be individually adjustable at the best condition in accordance with the height of each workpiece at each station.